Loop clamps for mounting and restraining a plurality of wires or pipes commonly have a cushion or lining extending around the loop. In general, the clamp cushion is a soft, rubber-like resilient material having either a smooth surface or raised nodes on one side of the lining surface. These raised nodes can take various uniform or irregular shapes including needle-like or sawtooth-like protuberances having a generally sinusoidal configuration.
In practice, the smooth, resilient lining provides point contact on the surfaces of the outer wires or pipes of a bundle. Thus, the bundle and its wires or pipes are not firmly secured and can rotate or work loose to cause possible damage or difficulty. Therefore, clamp cushions having a nodal or serrated configuration are preferred since they tend to grip the outer strands of wire between the nodal or serrated protuberances and thereby help to position and secure the individual wires more efficiently than would a flat surface cushion.
One type of widely used clamp cushion having a serrated configuration is the "sawtooth" clamp cushion. In addition to its improved ability to restrain and maintain a bundle of wires within a clamp device, the "sawtooth" clamp cushion has excellent vibration and noise damping characteristics when it is used on rigid tubing applications. The major drawback to the "sawtooth" cushion form is, however, its relatively high cost.
Clamp cushions are conventionally fabricated either by molding or by extruding the soft resilient material into a desired shape. For example, in the compression molding process, uncured rubber is placed into a mold. The mold is closed, thereby forcing the rubber into the final shape, and heat is then applied to cure the rubber. Alternatively, injection and transfer molding processes can be used. In the extrusion process, uncured rubber is forced through an opening that is shaped to the desired configuration and heat is then applied to the extruded rubber to cure it. The molding process is a batch-type process and is thus relatively slow and labor intensive. The extrusion process is continuous and faster than the molding process and fabrication of cushions by extrusion requires much less labor per part such that parts manufactured by the extrusion process are considerably less expensive than identical parts manufactured by the molding process. However, the fabrication of the serrated or "sawtooth" configuration of clamp cushions does not lend itself to the conventional extrusion process since the sawtooth-like protuberances are each at a 90.degree. angle to the direction of flow of the resilient material through the extrusion die. Prior to the present invention, therefore, "sawtooth" clamp cushions were generally fabricated as molded strips with the associated production drawbacks of using molds.
It is accordingly an object of this invention to provide a method of extruding soft resilient material to prepare a clamp cushion having a plurality of longitudinally spaced transverse nodes on the surface of the cushion at a lower cost and greater efficiency than in the conventional molding procedure.
It is another object of this invention to provide such a method wherein a clamp cushion having a serrated or "sawtooth" configuration is fabricated by a continuous and effective extrusion process.
Still another object of this invention is to provide such a method wherein the extrusion of clamp cushions having uniform or non-uniform sized serrations on the surface is cost-and labor-efficient.